Flu-like symptoms following botulinum toxin therapy.

This paper reviews the relevant literature on flu-like symptoms (FLS) in patients treated with botulinum toxin (BoNT) type A and B. We conducted a systematic search in PubMed and Medline of publications on BoNT and FLS. FLS were defined as the presence of symptoms of an upper respiratory tract infection associated with fever, general malaise or fatigue, within one month after BoNT injections and not secondary to any other identified condition. FLS have been reported in between 1.7 and 20% of patients treated with various preparations of BoNT/A. Most patients have a mild to moderate symptoms lasting less than 2 weeks, but 66 serious AEs related to FLS were reported to the Food and Drug Administration between 1989 and 2003. No significant differences in the frequency of FLS have emerged when different BoNT/A commercial products were compared, although no well-designed head-to-head comparison trials focusing on FLS have been published. For BoNT/B preparations, FLS have been reported in 5-55% of cases. We concluded that the frequency of FLS in patients treated with BoNT/A and BoNT/B varies widely between studies and no clear risk factors have been identified for this complication. We suggest potential treatments like analgesics/antipyretics or switching to less antigenic preparations in case of persistent symptoms.